The present invention relates to a turbo type fluid machine, and more particularly to detection of abnormality in a turbo type fluid machine provided with a dry gas seal.
In a turbo type fluid machine such as a multi-stage centrifugal compressor, in which a plurality of centrifugal impellers or semi-axial flow impellers are mounted to the same shaft, use of dry gas seals has been rapidly spreading in recent years in order to prevent a working gas from leaking into a lubricating oil used for bearings and from flowing outside the fluid machine. The dry gas seal normally comprises a primary dry gas seal for preventing the working gas from leaking to a side of bearings disposed in the atmosphere side from an inside of the compressor, and a secondary dry gas seal for serving as a backup when the primary dry gas seal is damaged and for preventing the working gas, which leaks from the primary dry gas seal, from leaking to the side of the bearings. Then, the state of the primary dry gas seal is monitored by checking the leaking of the working gas from the primary dry gas seal.
Concretely, there is provided a pipe, through which the working gas leaking from the primary dry gas seal is communicated with a space formed between the primary dry gas seal and the secondary dry gas seal, and the working gas is conducted to outside through the pipe. Such line is called as a primary dry gas seal vent line. An orifice is provided in the primary dry gas seal vent line to find pressure and a flow rate of the working gas, which flows through the primary dry gas seal vent line, from pressures before and after the orifice, whereby a flow rate of leakage is monitored.
Japanese Patent Unexamined Publication Nos. 4-29678 and 4-187897 describe examples of a system, which provides a primary dry gas seal vent line in a multi-stage centrifugal compressor in the above-mentioned manner to monitor an amount of a working gas leaking from the primary dry gas seal vent line. Further, Japanese Patent Unexamined Publication No. 7-208330 describes the provision of a primary gas seal and a secondary gas seal to prevent a working gas from leaking out of a machine or into a lubricating oil. Further, Japanese Patent Unexamined Publication Nos. 4-228975 and 6-174106 describe the provision of a pressure control valve and a flow meter in a seal gas supply flow passage in a screw compressor, in which dry gas seals are used, to issue an alarm when a gas flow rate becomes equal to or more than a predetermined value.
Since a primary dry gas seal constituting a dry gas seal effectively functions in normal operation, it is less possible that a secondary dry gas seal is directly acted by a pressure of a working gas. Therefore, an amount of leakage through the secondary dry gas seal is markedly less than that through a primary dry gas seal. In order to detect the small amount of leakage, it has been proposed to provide a flow amount meter such as an orifice or the like in the secondary dry gas seal vent line, by which the working gas leaking from the secondary dry gas seal is conducted outside the machine in the same manner as that for the primary dry gas seal. However, since the amount of leakage itself is small, measurement is actually difficult due to the need of extremely throttling an orifice used as the flow rate measuring means, and to the necessity of an expensive equipment capable of measurement with high accuracy in the case of a small amount of leakage even when a flow meter such as an electromagnetic flow meter is employed.
Further, if an orifice and a flow meter are provided in the secondary vent line, the working gas does not flow to the second vent line of a great flow-channel resistance but flows to a side of bearings disposed outside the secondary dry gas seal in the worst circumstances, in which both the primary dry gas seal and the secondary dry gas seal are broken. As a result, there is caused a risk of the working gas flowing into an oil return system of the lubricating oil in large quantities. In the case where the working gas is a combustible gas or include a poisonous component, flow of the working gas into the oil return system causes a risk of a serious accident generating. Accordingly, it is not desirable to provide in the secondary vent line a means, such as an orifice, a flow meter and the like, for presenting a channel-resistance. As mentioned above, since it is not desirable to provide a channel-resistance in the secondary vent line, direct monitoring of an amount of leakage from the secondary dry gas seal has been conventionally given up.
Hereupon, the secondary dry gas seal serves to prevent the working gas from leaking from the primary dry gas seal to the bearings and to serve as a backup when the primary dry gas seal is damaged, so that it is strongly demanded to correctly grasp the operating condition of the secondary dry gas seal with a view to increasing reliability for a turbo type fluid machine. With the respective prior art mentioned above, an adequate effect has been obtained with respect to securing of reliability and reduced cost of a dry seal, while an insufficient attention has been paid to correctly grasping an amount of leakage from the secondary dry gas seal for the reason mentioned above.
The invention has been devised in view of the disadvantages of the prior arts mentioned above, and has its object to improve reliability on a turbo type fluid machine. Another object of the invention is to improve reliability on a dry gas seal used in a turbo type fluid machine. A still further object of the invention is to provide a dry gas seal improved in reliability and having a simple structure.
To achieve the objects mentioned above, in a first aspect of the invention, there is provided a turbo type fluid machine provided with a sealing device composed of a primary dry gas seal and a secondary dry gas seal, the improvement wherein presence of abnormality on the secondary dry gas seal can be detected in accordance with an amount of a working gas leaking from the secondary dry gas seal. Preferably, the machine further comprises a flow rate switch for detecting an quantity of the working gas from said secondary dry gas seal is provided; and further comprises means for supplying a purge gas to said secondary dry gas seal, and pressure control means capable of controlling the purge gas supplied from the supply means to make the same substantially constant in pressure in the secondary dry gas seal.
To achieve the objects mentioned above, in a second aspect of the invention, there is provided a turbo type fluid machine provided with a rotor, bearings, which rotatably support the rotor and are arranged in the vicinity of both ends of the rotor, a casing, which receives therein the rotor and the bearings, and two sealing devices arranged inwardly of the bearings in an axial direction of the rotor, the sealing devices comprising a first fixed ring and a second fixed ring, which are fixed to said rotor, a first stationary ring opposed to the first fixed ring and fixed to the casing, a second stationary ring opposed to the second fixed ring and fixed to the casing, and a purge gas supply line, through which a purge gas is fed to opposing portions of the second fixed ring and the second stationary ring, the purge gas supply line being provided with abnormal flow-rate detecting means.
More preferably, the abnormal flow-rate detecting means is a flow rate switch; the machine further comprises control means provided in the purge gas supply line for controlling pressure of a gas flowing in the purge gas supply line; the pressure control means includes a control valve and a pressure transmitter provided downstream of the control valve; the pressure control means includes a control valve with a diaphragm; the machine further comprises a primary seal vent line provided on back sides of the first rotating ring and the first stationary ring for conducting a gas, which leaks from the first rotating ring and the first stationary ring, to outside the machine; and the machine further comprises an orifice, a pressure switch and a flow rate meter, which are provided in the primary seal vent line.
To achieve the objects mentioned above, in a third aspect of the invention, there is provided a dry gas seal device for sealing a working gas compressed in a turbo type fluid machine, comprising a primary dry gas seal and a secondary dry gas seal, the secondary dry gas seal including abnormality detecting means for detecting abnormality in accordance with an amount of the working gas leaking from the first dry gas seal. Preferably, the abnormality detecting means comprises purge gas supply means for supplying the purge gas to the secondary dry gas seal, pressure control means for controlling pressure in the purge gas supply means, and a flow rate switch for detecting abnormality in flow rate within the purge gas supply means.